Determining training effect (TE) by estimating Excess Post-Exercise Oxygen Consumption (EPOC) and activity class of a person is well-known prior art (see for example “EPOC Based Training Effect Assessment”, White paper by Firstbeat Technologies Ltd., February 2007). EPOC measures the quantity of exercise-induced disturbance of body's homeostasis using heart beat measurements, whereas TE indicates the effect of a single exercise session on improvement of cardiorespiratory fitness and fatigue resistance during a prolonged exercise. Activity class is an index which describes the activity level of the person and is used to individualize the determination of TE. Activity class is typically determined based on the classification of Shvartz & Reibold in 1990.
The method to assess TE as described in the above-references publication is commonly used in wearable sports monitoring devices, such as wrist-worn sports monitors.
The known method suffers from some disadvantages. First, it has been noted that the TE determined during sports performances with a certain type of intensity profile does not correspond to the actual physiological effect achieved. For example, in the case of an exercise with a high intensity period in the beginning and a constant lower intensity period in the end, the TE has been found not to change during the constant intensity period although the person feels that the training is still effective.
Second, the TE may not reflect the true physiological effect in the case of very long training sessions. For example, during a long low-intensity exercise, a user may not see the TE rise significantly although the stressfulness felt during the exercise would be relatively high.
Third, the TE determination during discontinuous training sessions, i.e. sessions with pauses, is not reliable.
Fourth, the TE does not take into account base endurance of an individual in all circumstances. Although common TE calculation methods utilize activity class given as an index number, the result may not be truthful, since there are many personal factors affecting the base endurance that cannot be fully described by a simple activity class index. These include for example trajectories and economy of movements and habituation to stress. The latter includes a plurality of sub-factors comprising for example cell metabolism, number of mitochondria, capability of cells to produce ATP, state of development of capillaries, hormonal factors, and capability of heart to circulate blood.
On the basis of the above, there exists a need for improved methods and apparatuses to estimate the effect of training in improving the fitness of individuals.